1. Field of the Invention
This invention relates to a screen printing apparatus, and more specifically to a screen printing apparatus which is capable of holding a squeegee thereof in a level state.
2. Description of the Related Art
Conventionally, a screen printing apparatus is known as one of printing apparatuses which print (coat) a printing material (coating material) formed by a thin piece such as a sheet of paper. In the screen printing apparatus, a squeegee slides on a screen having ink placed thereon from a printing start side to a printing end side whereby the printing material placed on a printing table is printed. Further, after the printing, a scraper slides on the screen from the printing end side to the printing start side to thereby scrape ink remaining on the screen back to the printing start side. And then, these operations are repeatedly carried out in an alternating manner to thereby print a plurality of printing materials in succession.
That is, in the screen printing apparatus, the printing table on which a printing material such as a sheet of paper is placed is arranged in a vertically movable manner, and a carrying gripper carries the printing material onto the table. During the printing, the printing material is held on the printing table by vacuum.
The screen which is masked in a predetermined manner is arranged over the printing table in a vertically movable manner. Above this screen, the squeegee and the scraper are positioned in a manner opposed to each other. The squeegee and the scraper are each arranged in a vertically movable manner such that each of them can be brought into or kept from contact with the screen. Further, the squeegee and the scraper are both horizontally movable above the screen.
As shown in FIG. 8, during the scraping process after the printing, the printing table 81 and the screen 82 have been moved away from each other. The scraper 83 has been moved to a position in which it is in lightly urging contact with the screen 82, whereas the squeegee 84 has been moved to a position away from the screen 82. In this state, the squeegee 84 and the scraper 83 are moved horizontally from the printing end side to the printing start side, whereby ink 85 remaining on a masking portion of the screen 82 is scraped away. The ink 85 scraped in this way is collected into a lump at the printing start side on the screen 82.
Then, in the printing process following the scraping process, as shown in FIG. 9, the screen 82 and the printing table 81 are moved toward each other, whereby the screen 82 is overlaid on the printing table 81. At this time, the squeegee 84 and the scraper 83 are switched in their positional relation relative to the screen 82. That is, during the printing process, the squeegee 84 is in lightly urging contact with the screen 82, whereas the scraper 83 is kept from contact with the screen 82. In this state, the squeegee 84 and the scraper 83 are moved horizontally from the printing start side to the printing end side, whereby the lump of the ink 85 is spread out over the screen 82 by the squeegee 84 and the spread ink 85 adheres to a printing material 86 through non-masking portions of the screen 82 to print the printing material.
When the printing is carried out as described above, conventionally, parallelism of the squeegee to the screen is adjusted before starting printing work. In case this adjustment of parallelism is not properly carried out, there occurs low printing pressure on one side of the squeegee, causing a blurred print, i.e. faulty printing. Further, conventionally, it is impossible to adjust printing pressure during a printing operation. Therefore, whenever such a faulty printing occurs, the printing is required to be stopped to adjust the parallelism between the squeegee and the screen, resulting in a degraded manufacturing efficiency or productivity.